Catch Block Node — Configuration

Properties Reference

Property	Type	Required	Default	Description
`error_variable_prefix`	string	Optional	`"__exception"`	The prefix used for the three exception memory variables injected by the catch handler. By default, variables are named `__exception_type__`, `__exception_message__`, and `__exception_stacktrace__`. Changing this prefix generates differently named variables — useful for distinguishing inner and outer catch scopes in nested try/catch patterns.

Default Variable Names

With the default prefix (__exception), the following memory variables are populated on catch:

Memory Variable	Type	Content
`$mem.__exception_type__`	string	The .NET exception class name (e.g., `HttpRequestException`, `TimeoutException`, `ArgumentNullException`)
`$mem.__exception_message__`	string	The exception's human-readable message property
`$mem.__exception_stacktrace__`	string	The full .NET stack trace string for debugging and log submission

Sample Configuration JSON

Default configuration (no prefix customisation needed in most cases):

{
  "nodeType": "CatchBlock",
  "id": "catch_payment_api",
  "label": "Catch — Payment API Errors"
}

With a custom prefix for nested catch disambiguation:

{
  "nodeType": "CatchBlock",
  "id": "catch_inner_email",
  "label": "Catch — Email Send Errors",
  "config": {
    "error_variable_prefix": "__email_error"
  }
}

With the custom prefix __email_error, the variables become:

$mem.__email_error_type__
$mem.__email_error_message__
$mem.__email_error_stacktrace__

Nested catch variable conflicts: When using nested try/catch blocks, always use a custom error_variable_prefix on the inner catch block. If both inner and outer catch blocks use the default __exception prefix, the inner catch's variables will overwrite the outer catch's variables in shared memory scope, making it impossible to distinguish which exception is being handled.

Common Exception Types

The following exception types are commonly encountered in BizFirstAI workflows:

Exception Type	Typical Cause	Recommended Handling
`HttpRequestException`	External API call failed (network error, non-2xx response)	Retry with backoff, log to error channel, use cached data
`TimeoutException`	External service did not respond within configured timeout	Retry once, then fallback or alert team
`KeyNotFoundException`	Expected dictionary key or map field was absent	Set default value, log warning, continue
`ArgumentNullException`	A required expression resolved to null	Log data quality issue, skip record, alert data team
`UnauthorizedException`	API credentials expired or invalid	Trigger credential refresh workflow, alert admin

Catch Block — Configuration

Properties Reference

Default Variable Names

Sample Configuration JSON

Common Exception Types